How did conflicting inheritance laws create a crisis in Schleswig and Holstein?

The crisis in Schleswig and Holstein was fundamentally driven by the fact that the succession laws of Denmark conflicted with those of the duchies.12

While the Danish monarch ruled both regions, the legal frameworks for inheritance differed, creating uncertainty regarding the status of the duchies upon the death of a king. This tension was exacerbated following the death of King Frederick VI in 1839. Because the Danish crown sought to maintain the integrity of the realm, it attempted to assert that succession laws should be uniform across all territories; however, this was undermined by rising nationalist passions.1

German nationalists argued that the duchies should remain linked and independent of Denmark, while Danish nationalists—specifically the Eider-Danes—insisted that the Eider River should serve as the national boundary, effectively incorporating Schleswig into Denmark and detaching it from Holstein. These conflicting legal and national aspirations turned the duchies into a persistent source of international contention, ultimately leading to the German-Danish War in 1864.312